The present invention relates to recycling and more particularly to the recycling of diverse pulp and paper products to provide a homogenous cellulosic feedstock having a plurality of beneficial uses.
Fossil materials are finite natural resources, and these materials are rapidly being consumed. The world is also facing many environmentally significant problems associated with the depletion of fossil materials, particularly petroleum, for the production of energy and petrochemicals. A variety of solid, liquid, and volatile organic compounds associated with petroleum extraction, transport, refining, and manufacturing operations have been and are continuing to be released into the environment. However, the most significant environmental factor is the release of carbon dioxide into the atmosphere during the burning of fossil fuels.
The use of fossil fuels has added tremendous quantities of carbon dioxide to the atmosphere. Since this carbon dioxide is being released from fossilized biomass long since effectively removed from the biosphere, there is currently insufficient plant life on earth to consume all of the carbon dioxide being produced. Therefore, the percentage of carbon dioxide in the atmosphere is increasing. Carbon dioxide and other "greenhouse gases" (e.g., volatile organic compounds) allow high energy, short wave length solar radiation to penetrate the atmosphere and to transfer heat to the earth's surface, but the same gases impede the low energy, long wave length radiation that dissipates the absorbed heat from the earth. Thus, heat from the sun is trapped in the earth's atmosphere, which is known as the "Greenhouse Effect." Reduction or elimination of the use of fossilized carbonaceous materials as combustion fuels would halt and possibly reverse current trends in altering the biosphere. The use of renewable biomass as a replacement for fossilized combustion fuels is a formidable task, but it is an environmentally beneficial task that is well worth the effort, especially when considering the long term effects of continuing current trends.
Another environmental concern facing today's earth is the production and disposal of waste, including municipal solid waste (MSW). The ability to recycle such waste productively and efficiently could significantly reduce the current volume of unused and discarded waste.
Municipal solid waste (MSW) includes, but is not limited to, cellulosic and/or noncellulosic materials such as office wastes, business wastes, institutional wastes, industrial wastes, residential wastes, pulp and paper products, inks, glues, plastics, glass, metals, food wastes, and yard wastes. Within MSW, the cellulosic component (e.g., pulp and paper components) accounts for a relatively large portion of MSW. Therefore, there has been a particular need to try to recycle and utilize the pulp and paper components to reduce the amount of MSW.
Many attempts have been made to use MSW for energy production in so-called resource recovery facilities. Some such facilities incinerate the MSW without any prior separation of potentially recyclable materials, with the possible exception of curb side or drop-off source recycling, to produce steam and/or electricity. These facilities are known as mass-burn incinerators, which are very expensive to site, permit, construct, and operate, in addition to producing large quantities of hazardous or toxic gases and airborne particulates, as well as large quantities of hazardous or toxic fly ash and sometimes bottom ash that must be landfilled. Some other such facilities use MSW that has been shredded with some non-combustibles subsequently removed prior to incineration for energy recovery, which are known as refuse derived fuel (RDF) incinerators. RDF incinerators tend to emit lesser amounts of hazardous or toxic air pollutants and to produce lesser amounts of hazardous or toxic ash than mass-burn facilities. Still other facilities use a combination of manual labor and mechanical devices to separate recyclable materials from the MSW, which are known as MSW materials recovery facilities (dirty MRFs). The non-recyclables from dirty MRFs are usually shredded and incinerated either on-site or off-site for energy recovery. The incinerator fuel from dirty MRFs produce lesser amounts of air pollutants and ash than either mass-burn or RDF incineration facilities. Some attempts have also been made to cap and recover the gases from MSW landfills for energy production. Landfill gas recovery and use does reduce the emission of greenhouse gases that would otherwise be emitted to the atmosphere, particularly volatile organic compounds from household and industrial chemicals in MSW and methane and carbon dioxide from anaerobic digestion of the putresible materials in MSW. Carbon dioxide from the incineration of chemically unaltered biomass (e.g., wood, yard wastes, and food wastes) and even chemically altered biomass (e.g., pulp and paper products, leather, rubber, and some other polymers of plants) does not result in a net increase in the concentration of carbon dioxide in the atmosphere, unlike fossilized biomass. The recent biomass, as opposed to fossil biomass, is renewable, since growing plants fix sufficient carbon dioxide into new biomass to essentially recycle the atmospheric carbon dioxide produced by their eventual decay or combustion. As pointed out earlier, combustion of fossilized biomass (e.g., petroleum, coal, etc.) does cause a net increase in atmospheric carbon dioxide.
The use of renewable plant biomass, including such materials as waste pulp and paper products in MSW, for producing solid, liquid, and gaseous fuels, chemicals, fertilizers, and other useful products, in addition to energy via direct combustion, would reduce or eliminate dependence on fossil materials and the unwanted secondary effects of the use of fossil materials as noted above, and, at the same time, would reduce unused and discarded waste.
In order to be able to fully utilize plant biomass to replace fossilized carbonaceous materials, it is necessary to transform the plant biomass, particularly woody biomass, into a form that is easily accessible to various chemicals, enzymes and/or microbes to convert the biomass into the desired end products. Natural biodegradation is an excellent means to break down plant biomass to its basic substituents, but the process is too slow to meet the demand for raw materials in industrialized societies. Therefore, if plant biomass is to be effectively used, it must be rapidly degraded.
Woody biomass is a hard substance that provides few points of entry for chemicals, enzymes and microbes to gain access to the composite molecules. The pulp and paper industry has already devised ways to at least partially break down the structure of woody biomass through mechanical size reduction and chemical treatments, but since the desired end products of this industry must retain a fibrous consistency with tensile strength and rigidity, additional treatments are necessary to transform these pulp and paper products into a homogenous cellulosic feedstock suitable for the final molecular breakdown into other useful products, such as fuels, chemicals and fertilizers.
The fibrous materials of pulp and paper products have been obtained from wood. Wood, like other plant materials, is a product of a biological process known as photosynthesis, in which plants consume simple inorganic minerals, carbon dioxide and water using sunlight as an energy source, and metabolically manufacture all of the different types of organic molecules consistent with living organisms. Photosynthetic organisms, mostly green plants, are at the top of the food chain, and they also yield oxygen as a by-product of the photosynthetic process. Such plants are not only a source of food and fiber for all other living organisms, but they also consume a greenhouse gas, carbon dioxide, and emit oxygen, which is required by all living organisms, including photosynthetic plants for metabolic "combustion" of carbonaceous molecules called respiration.
Respiration is a metabolic process whereby organic molecules serve as food from which living organisms extract the solar energy entrapped in the chemical bonds of the molecules for life processes while consuming oxygen for the oxidation or combustion of the food and emitting carbon dioxide and water as by-products. The principal and most abundant type of organic material of plant biomass is the structural component called lignocellulose. This material is composed mostly of three distinct biopolymers: cellulose, hemicellulose and lignin. These biopolymers are an abundant source of renewable energy and carbonaceous material that can and will eventually replace fossilized materials for the production of fuels, chemicals, fertilizers, and energy.
Prior attempts have been made and a few processes have been developed to separate pulp and paper products from commingled mixtures of waste and to break down the pulp and paper products to its substituents for varied uses. Previous methods have relied on physical shearing of such materials to simply reduce the particle size. There are a variety of these so-called "dry" methods that subject these materials either to high-speed hammer mills or low-speed grinders to produce a fairly uniform particle size ("fluff"). This fluff is usually prepared from waste, such as MSW, and after separation of dense materials, such as glass, grit, ferrous metals, and high moisture contaminants that have also been reduced in particle size during the shredding process, the dry fluff is used as "refuse derived fuel" for direct combustion to produce energy.
Another so-called "wet" method utilizes a device called a hydropulper, which is the equivalent of a large kitchen blender, to shred such materials suspended in a large volume of water. This is a popular method used by the pulp and paper industry to reduce the particle size of such materials so that it may be recycled into the manufacture of new pulp and paper products.
These methods do yield pulp and paper products of a fairly uniform size, but none of these methods is intended to, nor do they, alter the basic molecular structure of the cellulosic fibers of the pulp and paper materials to facilitate the intercalation of chemicals, enzymes, or microbes into the structure to bring about a more efficient and complete breakdown of the polymeric molecules comprising the fibrous materials.
A brief summary of the prior art attempts and other processes that involve processing of wastes and other materials follows.
U.S. Pat. No. 5,427,650 to Holloway discloses an apparatus and method for separation, recovery, and recycling municipal solid waste and the like by introducing solid waste materials into a rotatable pressure vessel, rotating, pressurizing, adding pH controlling chemicals and heating the pressure vessel and thus the waste material while simultaneously applying a mixing action to the solid waste material. Further, a vacuum is applied to the vessel to control the moisture content of the final fine organic portion of the process material.
U.S. Pat. No. 4,844,351 to Holloway discloses a method for treatment of mixed waste containing various plastics, such as municipal solid wastes, in which mechanical agitation and heat distortion of plastic films cause rupture and spilling of the contents of plastic film containers in the waste. The operating temperature of the process is in the range of about 195.degree. F. to 215.degree. F.
U.S. Pat. No. 4,540,495 to Holloway discloses a process for treating municipal solid waste material in the presence of moisture for the separation and recovery of inorganic matter and organic matter wherein the waste material is fed into a pressured chamber and is agitated therein. The contents of the pressure chamber are subjected to heat under a pressure for a predetermined period of time to cook, sterilize and soften the organic matter contained therein. The moisture content of the waste material is controlled so that the fines of the organic fractions have a residual moisture content ranging from about 60% to 70%.
U.S. Pat. No. 4,342,830 to Holloway discloses a process for recovery of organics and inorganics from waste material with a specific object of preparing the separated organic fraction for the production of ethanol wherein rigid organic matter becomes soft when subjected to heat and pressure. The process is carried out by feeding the waste material into a perforated container mounted within a closed chamber. The container is then agitated by suitable means, such as by rotation, as the chamber is subjected to pressure and heat to sterilize the waste material and soften the organic matter contained therein. The chamber is then depressurized wherein the softened organic matter is forced out of the container through its perforation, leaving only inorganic matter therein. The softened organic matter is shredded and broken up as it is forced through the perforations of the container.
U.S. Pat. No. 5,119,994 to Placzek discloses an apparatus and method for processing medical waste materials comprising an elongate pressure vessel having an inlet end, and a closely fitting inlet closure member. Moisture and heat are utilized to aid the processing of the waste.
U.S. Pat. No. 4,974,781 to Placzek discloses a method and apparatus to affect the separation of component fractions from paper-containing and plastic-containing waste materials. The method utilizes a rotating vessel equipped with lifting paddles and directional flighting. Moisture and heat are added in the process to effect repulping of paper materials.
U.S. Pat. No. 5,556,445 to Quinn et al. discloses a method for treating solid municipal waste material including placing solid municipal waste in a rotating chamber having an interior at ambient pressure, heating the waste at ambient pressure, and controlling the moisture content of the waste.
Russian Pat. No. 278406 discloses a process for treating wood chips within an agitating container at a temperature of 100.degree. C. with saturated steam at 110 C. in the complete absence of air and at a relative humidity of 40%.
European Pat. No. 0 407 370 A2 to Richter discloses a method and apparatus providing for the continuous digestion of comminuted cellulosic fibrous material (e.g. wood chips) to produce paper pulp, with increased sulfidity.
U.S. Pat. No. 5,198,075 to Nivelleau de La Bruniere et al. discloses a method of digesting lignocellulose materials impregnated with solutions of hydroxides or salts of alkali or alkaline earth metals.
U.S. Pat. No. 4,632,729 to Laakso discloses a method and apparatus for effecting presteaming and deaeration of wood chips, or like, comminuted cellulosic fibrous material. The method utilizes a vertical presteaming vessel and a second vessel for deaeration.
U.S. Pat. No. 5,164,042 to Larsen et al. discloses a method of producing high-yield pulp from pulp chip material containing lignocellulose. The pulp chipped material is treated with steam in a steam treating station for driving air out of the material and heating the material. The heat treated material is then mixed in a mixing station with a liquid containing chemicals.
U.S. Pat. No. 5,470,433 to Brodersen et al. discloses a process for the delignification of cellulose fiber plant raw material for the production of pulp using separate impregnating and delignifying stages, each using alcohol and alkali.
U.S. Pat. No. 5,624,616 to Brooks discloses a method for making lignocellulose fibers, which may be optionally coated with a suitable thermoplastic, wherein the starting materials may be chosen from a wide variety of generally non-recyclable contaminated wood, paper, and/or plastic products. A mixture of the preferred lignocellulose material characterized by a relatively low moisture content and the desired thermoplastics is refined and comminuted in a steam atmosphere which is at a temperature, pressure, and duration sufficient to soften both the lignin within the wood chips and the thermoplastic polymer. The temperature of the steam atmosphere is relatively high, at least about 170.degree. C., because of the use of dry wood chips which do not result in excessive vaporization during heating. The method also uses a steam pressure of at least 100 psig.
U.S. Pat. No. 5,176,793 to Kurtz discloses a method for treating wood-fiber pulp, particularly pulp which contains recycled paper. The pulp is dewatered and then heated by means of super heated steam under pressure prior to being passed to a disburser in which the pulp is finely divided. The pulp is then passed from the disburser to a plug-outfeed screw.
U.S. Pat. No. 4,999,084 to Lang et al. discloses a method for removing wax particles from short fiber fractions, which have been separated from long fibers.
U.S. Pat. No. 5,137,599 to Maxham discloses a process for the production of paper making fiber or a pulp from waste solids emanating from pulp and paper mills, particularly waste solids and processed water streams.
U.S. Pat. No. 5,391,261 to Van Den Bergh discloses a method of bleaching de-inked pulped and removing the ink polar particles with steam.
U.S. Pat. No. 5,262,003 to Chupka et al. discloses a process of preparing a suspension of paper making fibers in water for use in the making of paper.
U.S. Pat. No. 4,872,953 to Smith discloses an apparatus and method for improving the quality of paper manufactured from recycled paper stock with comprises a hydrokinetic amplifier, a pulper, a dump chest, a cyclone separator, a pressure screen, a vibratory screen and a holding tank.
U.S. Pat. No. 5,122,228 to Bouchette et al. discloses a method of treatment of waste paper or the like at high temperatures in the range of 160.degree. C. to about 230.degree. C. The furnish is treated in a digester with or without added chemicals but in the presence of saturated steam. The preferred dwell times are in the range of about 1 minute to about 6 minutes. The treated furnish is then discharged from the digester, preferably, but not exclusively by an explosive discharge.
U.S. Pat. No. 4,312,701 to Campbell discloses a method for defibrating waste paper and disbursing contained asphalt and wax contaminates within the fibers. The waste paper is initially pulped with water and the resulting stock is then contacted with a high pressure stream of steam having a velocity in the range of 1200 to 1600 ft/sec. The mixture of steam and stock is passed through a mixing tube under highly turbulent conditions to defibrate the waste paper and disburse any asphalt, waxes, and other contaminates throughout the separated fibers. The resulting stock can be used in paper making processes, particularly for the production of paper board products.
U.S. Pat. No. 3,057,769 to Sandberg discloses a process of making paper of uniformed appearance free from normally visible spots from waste paper stock carrying bituminous material. The process uses a paper beater for disintegrating the stock, and makes a slurry of 0.7 to 1% of fiber in water.
U.S. Pat. No. 4,297,322 to Liu discloses equipment and method for treating solid waste in which a non-oxidizing atmosphere is provided through which the shredded solid wastes falls freely, unsupported and non-contacted, to prevent fusion of the plastics with each other, with other materials in the solid waste, or with the walls or components in the treating equipment. The process operates at temperatures of about 600 to 900.degree. F.
U.S. Pat. No. 4,325,707 to Burke, Jr. discloses a method and apparatus for treating solid municipal waste or other material within a pressure vessel which is pressurized with steam or a compressed gas. The pressure vessel is referred to as a "cannon" because the pressure vessel has a hinged mussel closure which can be opened rapidly by the pressure inside the vessel so that the solid material passes through the opening created.
U.S. Pat. No. 3,741,863 to Brooks discloses a method of providing cellulosic fibers and fiber bundles from sources of waste material, such as municipal and industrial waste products, for making medium density fiber board and/or paper. The process is a dry process utilizing the cellulosic products present in municipal and household waste. The waste is pulverized into small pieces, where after it is dried to remove excess moisture, and also for sterilization. After separating the cellulosic material from the other constituents of the waste, the cellulosic material is heated in the presence of a non-flammable medium, such as steam, to raise the temperature thereof and to affect further sterilization.
U.S. Pat. No. 4,540,467 to Grube et al. discloses a method and apparatus for the removal of mold core material from metal castings and for fragmentation of municipal waste material, e.g., paper products, involving heating and hydrating the materials within a pressure vessel. Chemicals active on the material to be processed or the hydration water are added during hydration to soften the material to be removed or fragmented. Excess liquid in the vessel is drained and pressurized steam is added for a selected period of time. A suitable temperature and pressure are achieved such that the moisture or liquid carried by the processed material will rapidly turn to steam or vapor when the pressure in the vessel is rapidly reduced by quickly opening and unloading means at the bottom of the pressure vessel. The sudden release of pressure (explosive) in the vessel causes the moisture to change to steam and a certain portion of the liquid in the material to flash to vapor in accordance with thermodynamic laws. The resulting rapid expansion within the processed material fragments it.
U.S. Pat. No. 4,079,837 to Grube et al. discloses a method for the separation of components of solid wastes which has been treated by thermal explosive decompression followed by biodegradation (also referred to as composting). The explosive decompression and composting pretreatment before separation presents a granular and inoffensive finely-divided product mixed with less fragmented nonbiodegradable materials such as plastic, metals and other substances. The method first separates the finely-divided product from the waste to leave a first residue, then magnetically separates any magnetic components from the first residue to leave a second residue, and then separates by gravity floatation any plastic components from the second residue, each step being carried out successfully without any interruption for further treatment of the waste.
U.S. Pat. No. 4,461,648 to Foody discloses a method for increasing the accessibility of cellulose in lignocellulosic materials to chemical or biochemical reagents. The method has extremely high operating pressures, 250 to 1000 psig, and has a purging step while the materials are under pressure.
Accordingly, it has been one objective of this invention to provide improved processes for transforming diverse pulp and paper products into a homogeneous cellulosic feedstock.
Another objective of the invention has been to provide processes for the volume reduction of municipal solid waste (MSW). A further objective of the invention has been to provide processes for reducing the volume of MSW while producing components during that process for use as replacements for fossil material.
Still another objective of the invention has been to provide an improved process for transforming diverse pulp and paper products into a homogeneous cellulosic feedstock useful for conversion into fuels, chemicals, fertilizers, and other useful products.